Many large work machines, such as off-highway mining trucks, front shovels, and hydraulic excavators, include numerous moving parts that require proper lubrication to prevent premature failure. Critical areas such as wheel bearings and linkage joints are advantageously lubricated during operation to eliminate the need for stopping the machine for lubrication. To prevent premature failure, these critical areas must be frequently lubricated, e.g. it may be advantageous in some environments to lubricate the critical areas as frequently as every 5-10 minutes. Since many of these machines have enormous operating capacities, time in which the machine is not operating represents a substantial loss of capacity to the owner. Obviously, if the machine must be lubricated every 5 minutes, the machine would be stopped for lubrication as much as it was operating.
To address these needs, various systems have been developed to provide lubrication during machine operation. Generally, such lubrication systems include an air system supply line, a solenoid air valve operated in response to a control, an air-powered lubrication pump, and an injector bank located at each of the critical areas of the machine. The lubrication control typically provides a timer designed to inject lubricant into the critical areas at preset time intervals during machine operation. While such systems provide adequate lubrication, they also tend to lubricate more often than necessary since it reacts solely to time and not to the actual use of the bearings or joints. For example, if a truck is standing still, there is no need to lubricate the wheel bearings during each time interval. It is only after the truck has been moving for the predetermined time interval that lubrication is required. Thus energy and lubricant could be conserved if the lubrication system is controlled in response to the length of time the bearings are actually being used rather than in response to time alone.
Another problem arises if there is a fault condition in the lubrication system. For example, if a lubrication line is broken or has become unattached,lubricant will not reach the desired location. To address this problem, prior art systems have provided pressure switches to be activated in response to the pressure in the lubrication lines reaching a predetermined level. If the pressure does not reach that level when the lubrication system is activated, an alarm is energized to indicate that a fault condition exists. However, merely indicating that the desired pressure was not reached is insufficient information for service personnel to efficiently diagnose and repair all types of problems. It may also be important to indicate whether the lubrication system pressure has exceeded a high pressure level. For example, if a lubrication line is obstructed or if the air pressure system is operating at too high of a pressure, the lubrication system pressure will exceed the predetermined level but there will nonetheless be a fault condition. Similarly, there may be a fault within the pressure sensor itself or the wire carrying the electrical signal from the pressure sensor may be shorted to ground or to the positive supply voltage. Information regarding which of the numerous possible fault conditions in the lubrication system and pressure sensor would be extremely useful to service personnel and would reduce downtime considerably.
Some prior art lubrication systems have provided adaptability to the system by using set-screws on the timer to adjust the time between lubrication and on the pressure switch to adjust the predetermined pressure level. Such adjustments, while helpful, inadequately address the full range of adaptability and precision desired for proper lubrication control. For example, it is beneficial to provide a more precise method of setting these parameters and to provide a means for adjusting the duration of each lubrication event.
The present invention is directed to overcoming one or more of the problems set forth above.